var ImgNum = 0;
var ImgLength = arrImages.length - 1;

var delay = 3000;

var lock = false;
var run;

function chgImg(direction) {
  window.clearInterval();

 if (document.images) {
  ImgNum = ImgNum + direction;
  if (ImgNum > ImgLength) {
   ImgNum = 0;
  }
  if (ImgNum < 0) {
   ImgNum = ImgLength;
  }
  document.slideshow.src = arrImages[ImgNum];
 }
}

function auto() {
 if (lock == true) {
  lock = false;
  window.clearInterval(run);
 }
 else if (lock == false) {
  lock = true;
  run = setInterval("chgImg(1)", delay);
 }
}